In the past few weeks, our entire planet has been experiencing an unprecedented crisis due to the COVID-19 pandemic, with extremely significant losses on many levels.

I am a professor of biology at the University of West Attica in Greece, and a volunteer at Greenpeace. Given the tremendous impact of this pandemic on people’s lives combined with the fact that many experts believe that global heating and other environmental disturbances could facilitate the development of more novel viruses such as COVID-19, I would like to explain how climate change relates to the transmission and spread of infectious diseases.

A heating planet might increase the frequency of infectious diseases

Rising global temperatures, coupled with the increasing frequency of extreme weather events, are predicted to cause changes in the seasonality, geography and intensity of infectious diseases.

Image of heat wave in Seoul illustrating global warming
A view of a building in Seoul during a summer heat wave.

Floods can enhance the spread of infectious agents like insects, bacteria, and viruses. Increasing temperatures and humidity affect the development, survival and spread of not only pathogens but also their hosts (often animals). Mosquitos and other insects that are carriers of diseases like malaria, dengue fever and the West Nile virus will move to areas of the planet that are colder today, as they warm up.

The West Nile virus, for example, first appeared in the northern hemisphere in New York, after a prolonged period of high temperatures followed by heavy rainfall in 1999. As Stanford University professor of biology Erin Mordecai has pointed out, “wealthy,  developed countries such as the US are not immune”.

Human intervention in the environment is impacting our health worldwide

Monkeys dig some food from the trash bins end up eating plastic thrown by the tourists of Batu Caves, Malaysia. Greenpeace volunteers and suppoters hold a waste clean-up at Batu Cave, Malaysia during Earth Day event to show their care to the nature and religious place.  Greenpeace is calling for the people in Malaysia to start reducing the use of single-use plastic. Batu Caves is a an iconic and popular tourist attraction in Selangor. A site of a Hindu temple and shrine, It also attracts thousands of worshippers and tourists, especially during the annual Hindu festival, Thaipusam
Monkeys dig some food from the trash bins end up eating plastic thrown by the tourists of Batu Caves, Malaysia.

According to the United States Agency for International Development, about 75% of all emerging and re-emerging infectious diseases are zoonotic – meaning they come from animals. These include, among others, SARS, H5N1 avian flu, and the H1N1 influenza virus. An increasing number of animal carriers of diseases are changing their behaviour and migrating to new areas due to climate change and habitat loss.

This, coupled with our search for alternative sources of food to meet our needs, increases the chances that humans will come into contact with animal carriers and become infected. Human intervention in the environment, like the massive deforestation of the Amazon, not only causes a decrease in biodiversity but also forces many wild animals to find new habitats, driving them closer to populated areas and into close contact with humans. 

This creates opportunities for pathogens to move from animals to humans and significantly increases the likelihood of epidemic outbreaks. 

Thriving ecosystems can help to stop the spread of epidemics

Large areas of intact natural habitats act as natural barriers that separate humans and wild animals and keep them safe from one another. 

A bat flies over Um island, famous as Bats Island in Sorong, West Papua.
A bat flies over Um island, famous as Bats Island in Sorong, West Papua.

A rich diversity of wild animal populations stems the spread of epidemic diseases, known as the “dilution effect.” This is because the higher the species variation, the lower the density of potential hosts for a virus. Species variation decreases the number of highly-susceptible populations in a species, which lowers the probability of transfer to humans.

But disrupting those ecosystems can make us more susceptible to getting diseases 

picture showing deforestation for farming and agriculture in chaco province in Argentina
The Gran Chaco is the second largest forest in South America, after the Amazon. The last 30 years, Argentina lost 8 million hectares of forests by intensive livestock farming and agriculture.

“The disruption of pristine forests driven by logging, mining, and rapid urbanisation is bringing people into closer contact with animal species they may never have been near before.” According to Kate Jones, chair of ecology and biodiversity at University College London, 

“We invade tropical forests and other wild landscapes, which harbor so many species of animals and plants — and within those creatures, so many unknown viruses. We cut the trees; we kill the animals or cage them and send them to markets. We disrupt ecosystems, and we shake viruses loose from their natural hosts. When that happens, they need a new host. Often, we are it.

The World Health Organization is reporting on how transmission patterns of infectious diseases will change as a result of climate change. There is a need to learn more about these complex cause-and-effect relationships and apply this information using integrated models to predict, as far as possible, the future impacts of climate change on the transmission and spread of infectious diseases.

We have a chance to build the world that we want to see in the wake of this disaster 

Enforced physical distancing is making us self-sacrifice for the greater good. Even though this crisis is physically pushing some of us further apart, we are seeing community bonds tightening, as people do what is necessary in this health crisis. 

There is a risk that any actions that governments have taken to promote a green transition may be undermined by the global financial crisis resulting from the coronavirus pandemic. Governments need to take radical actions to build the world we want to see once this is over.

Hundreds of young protesters marched through Central Tokyo to demand urgent action to prevent climate change. The demonstration is part of the global movement known as Fridays for Future.
Hundreds of young protesters march through Central Tokyo to demand urgent action to prevent climate change (November 2019). The demonstration is part of the global movement known as Fridays for Future.

In these dark and difficult times, it is worth mentioning the recent words of Bill McKibben on CNBC, “If the lesson learned is, let’s get back to the status quo ante, then the virus will probably slow down the energy transition. If the lesson learned is you have to take the physical world and its risks seriously, it could make governments more likely to move fast-especially since interest rates in much of the world are now effectively zero.”

Lia Patsavoudi is a Professor of Biology at the University of West Attica, and a volunteer with Greenpeace Greece. 

Further reading:

  1. What could warming mean for pathogens like Coronavirus? by Chelsea Harvey, Scientific American March 9, 2020.
  2. How Climate Change is Exacerbating the Spread of Disease by Renee Cho. State of the Planet. Earth Institute, Columbia University, 2014.
  3. How does climate change affect disease? by Rob Jordan, Stanford Woods Institute for the Environment, 2019.
  4. Deforestation and threats to the biodiversity of Amazonia. IC Vieira et al. Braz. J.Biol.68, 949-956, 2008.
  5. Climate change and infectious diseases, World Health Organization 2020.